Italy was among those countries who expelled the Syrian ambassador to Rome last month in a coordinated action with other Western powers after a massacre in the town of Houla.

The Syrian leadership "is fighting for its survival with an ever more direct and brutal escalation, with terror against the civilian population and with the artificial fuelling of internal conflict," Mr Terzi said.

His strong comments came as Assad appointed Riad Hijab as new prime minister - tasking him with forming a government - as armed rebels continued to go on the offensive in and around Damascus.

France characterized the appointment was a "masquerade."

Bernard Valero, a foreign ministry sopkesman said Assad "remains stubbornly deaf to the demands of his people."

Hijab's appointment of comes after a new parliament was voted in on May 7 in elections boycotted by opposition groups.

A former agriculture minister, Hijab, 46, replaces former premier Adel Safar, who had formed his government in April 2011, one month after an Arab Spring-inspired uprising erupted across Syria.

According to the Britain-based Syrian Observatory for Human Rights, more than 13,500 people, mostly civilians, have been killed in the 15 month uprising.

Hijab was born in Syria's eastern Deir Ezzor province and holds a PhD in engineering. He was appointed minister of agriculture in April 2011.

Meanwhile, local opposition activists said violent clashes broke out in the Damascus suburb of Harasta overnight between regime troops and rebel forces.

The battles were "violent," the monitoring groups said, adding "rebel forces clashed with troops at military intelligence headquarters and at a checkpoint."

Rebel forces also reportedly clashed with regime troops at checkpoints near Douma, Irbin and Zamalka, all in the Damascus region.

Battles and shootings also erupted in several other neighbourhoods of the capital, including Tishreen.